Fuel dispensers are equipped with a unit for measuring the volume of fuel dispensed. This unit, also known as a measurer, is generally a mechanical positive displacement meter.
The function of a mechanical measurer is to convert the flow of the fuel into a rotary motion in which one complete revolution corresponds to a given volume of fuel passing through the measurer. In a known piston type measurer for example, the liquid from the pump of the dispenser is injected into two or four cylinders which are filled and emptied in succession by means of a dispensing slide valve device. The pistons drive a crankshaft whose angle of rotation is proportional to the volume of liquid that has passed through the cylinders. An optical or magnetic encoding system coupled to the rotary motion supplies an electrical signal made up of a series of pulses each of which corresponds to a volume measurement increment, for example 1 centiliter (cl).
Piston and cylinder volume meter technology is well established and proven but nevertheless has a number of drawbacks, namely:
many mechanical parts, PA1 close machining tolerances, PA1 large overall size, PA1 moving parts subject to wear by friction that must be compensated by periodic calibration, PA1 problems concerning the ability of the materials used to withstand the chemical constituents of fuels, PA1 mechanical noise, PA1 high internal volume so that it is not possible to meter a plurality of different products sequentially in the same meter.